The formation of InSb quantum dots within a GaAs0.51Sb0.49 matrix lattice matched to InP is investigated. We show that the deposit of InSb on GaAs0.51Sb0.49 alloy surface, allows the achievement of a high density of InSb islands without dislocations. A strong dissolution of InSb quantum dots occurs during the capping with a GaAsSb layer. Reflection high energy electron diffraction analysis shows that InSb island dissolution occurs during the growth interruption under As and Sb. We propose a procedure based on the deposit of a thin GaSb capping layer on top of InSb islands to prevent the As/Sb exchange. Optical properties are investigated using photoluminescence. Electronic properties are discussed within an improved tight-binding model.